If you're looking to pick up an add-on battery, we've demystified the impenetrable gadget lingo to explain what you should look for, what to avoid, how much capacity you'll want and other factors to consider when trying to keep your kit charged up on the road.

Oh mAh, what are the units?

First up, you'll want to know how much charge you need. Batteries are usually measured by the current standard unit of electrical charge – which is the milliampere-hour, abbreviated "mAh".

Phone manufacturers can be cagey about battery size but most smartphones sit somewhere between 1400 and 2200 mAh.

The ifixit webite, best known for its revealing teardowns of mobile phones, says that the iPhone 4's battery is 1432 mAh, iPhone 5's is 1440 mAh and Samsung Galaxy S III's is 2100 mAh.

The latest iPad's battery, by contrast, is just under 12,000 mAh according to ZDnet.

Price guides

Work on the idea that you'll spend about A$30 for 1000 mAh, A$40 for 2000 mAh, A$60 for a 4000 mAh charger and on up.

That's at Australian big-box retailers, and you might save $10-20 at the high end by picking one up overseas or in duty free.

Check the connection plugs

As any iPhone user upgrading to the iPhone 5 will be realising, it's a bad idea to lock yourself into a specific connector for accessories.

Instead, get one that pumps out power via USB, and connect the charging cable you got with your phone or other device to it.

If you want to charge more than one device -- a 3G pocket wifi device as well as your phone, say -- look for a battery with two USB sockets.

Check also that the charging connector to juice up the battery itself isn't something randomly proprietary either.

We'd suggest mini-USB or micro-USB are the best to look for, unless you're going for a seriously massive external battery (10,000 mAh or more), where you'll want to plug it straight into the wall via its own adapter.